1. Field of the Invention
The present invention pertains to a bypass valve assembly which, while adaptable for various purposes, is especially useful in testing systems for monitoring the pressure in a fluid flow-line and closing off such fluid flow-line upon detection of pressures of predetermined values. Too great a pressure drop in such a flow-line might indicate a break in the line, while a substantial increase in pressure generally indicates some type of obstruction. In either case, the flow in the line should be cut off until appropriate corrective measures can be taken.
Accordingly, such a system typically comprises two pressure control units communicating with the flow-line. A shut off valve in the flow-line is maintained in open position by the communication of fluid pressure to its actuator through a signal line. The signal line passes through both control units. If the pressure becomes too great in the flow-line, this will be detected by one of the units which will close the signal line. This in turn will cause the actuator to close the shut off valve. Similarly, if the pressure becomes too low, the other unit will close the signal line and thus cause the shut off valve to be closed.
2. Description of the Prior Art
In connection with systems of the type described above, it is necessary periodically to test the control units to be sure that they are operating properly. This necessitates blocking the control units from communication with the pressure in the flow-line and applying a known test pressure to the control units. However, it is not desirable to have the control units close the signal line thereby causing closing of the shut off valve in response to the test pressure. Therefore, a bypass line, not controlled by the control units, is provided for supplying fluid pressure to the shut off valve actuator during the testing procedure.
In conventional systems, such test procedures require the operation of three separate valves: one to block the communication between the control units and the flow-line, one to admit the test pressure to the control units, and one to open the by-pass line to the shut off valve actuator. Since these valves are usually not located near one another, the procedure generally requires two workers or necessitates several trips back and forth between the valve locations on the part of one worker. Furthermore, regardless of the location of the valves, there is always the danger that, once the testing is completed, the worker will forget to disconnect the bypass line and re-connect the signal line. Thus, although the control units may be working properly, they will not effect closing of the shut off valve since fluid pressure will be continuously supplied to its actuator through the bypass line. Thus, the purpose of the monitoring system is frustrated.